Microporous solids such as molecular sieves (e.g., zeolites) are often synthesized using a xe2x80x9cstructure directing agentxe2x80x9d (SDA). The SDA apparently assists in organizing the atoms of the molecular sieve into a particular crystalline topology. The SDA may typically be an organic amine, quaternary ammonium compound or organometallic compound. Once the microporous solid is synthesized, the SDA is in the pores of the microporous solid and is quite often spatially trapped. In order to remove the SDA from the pores, the microporous solid is normally heated to a very high temperature, i.e., calcined, to decompose the SDA and release the smaller decomposition produces from the pores. However, calcination can have deleterious effects on the microporous solid, and destroys the SDA, preventing its reuse. Calcination may also cause environmental problems due to the effluent gases formed.
It would, therefore, be desirable to be able to remove the SDA from a microporous solid without having to calcine it. It would also be desirable to be able to recover the SDA in a form such that it can be reused.
In accordance with the present invention, there is provided a method of removing a structure directing agent from a microporous solid at a temperature below the temperature that would cause the structure directing agent to decompose comprising cleaving the structure directing agent within the pores of the microporous solid, at a temperature below the temperature that would cause the structure directing agent to decompose, into two or more fragments and removing the fragments from the pores of the microporous solid at a temperature below the temperature that would cause the structure directing agent or its fragments to decompose.
Further provided in accordance with the present invention is a method of removing a structure directing agent from a porous molecular sieve at a temperature below the temperature that would cause the structure directing agent to decompose comprising cleaving the structure directing agent within the pores of the molecular sieve, at a temperature below the temperature that would cause the structure directing agent to decompose, into two or more fragments and removing the fragments from the pores of the molecular sieve at a temperature below the temperature that would cause the structure directing agent or its fragments to decompose. Preferably, the SDA is decomposed into fragments that can be recombined ex situ for recyclable use.
The present invention also provides a method of making a porous, crystalline molecular sieve comprising:
(a) preparing an aqueous solution from (1) sources of an alkali metal oxide, alkaline earth metal oxide or mixtures thereof; (2) sources of an oxide selected from the oxides of aluminum, iron, gallium, indium, titanium, or mixtures thereof; (3) sources of an oxide selected from oxides of silicon, germanium or mixtures thereof; and (4) a structure directing agent capable of forming the molecular sieve;
(b) maintaining the aqueous solution under conditions sufficient to form porous crystals of the molecular sieve which contain the structure directing agent in the pores; and
(c) cleaving the structure directing agent, at a temperature below the temperature that would cause the structure directing agent to decompose, into two or more fragments and removing the fragments from the molecular sieve at a temperature below the temperature that would cause the structure directing agent or its fragments to decompose.
The present invention also provides a method of making a porous, crystalline molecular sieve comprising:
(a) preparing an aqueous solution from (1) sources of an alkali metal oxide, alkaline earth metal oxide or mixtures thereof; (2) sources of an oxide selected from the oxides of aluminum, iron, gallium, indium, titanium, or mixtures thereof; (3) sources of an oxide selected from oxides of silicon, germanium or mixtures thereof; and (4) a structure directing agent capable of forming the molecular sieve; and (5) an amine component comprising at least one amine containing one to eight carbon atoms, ammonium hydroxide and mixtures thereof;
(b) maintaining the aqueous solution under conditions sufficient to form porous crystals of the molecular sieve which contain the structure directing agent and the amine component in the pores;
(c) removing the amine component from the pores of the molecular sieve at a temperature below the temperature that would cause the structure directing agent or the amine component to decompose; and
(d) cleaving the structure directing agent, at a temperature below the temperature that would cause the structure directing agent to decompose, into two or more fragments and removing the fragments from the molecular sieve at a temperature below the temperature that would cause the structure directing agent or its fragments to decompose.
Further provided by the present invention is a method of making a microporous solid comprising:
(a) preparing a reaction mixture comprising at least one active source of reactants required to produce the microporous solid, a structure directing agent capable of forming said microporous solid, and sufficient water to shape said mixture into a self-supporting shape;
(b) heating said reaction mixture at crystallization conditions and in the absence of an external liquid phase for sufficient time to form the microporous solid containing the structure directing agent; and
(c) cleaving the structure directing agent, at a temperature below the temperature that would cause the structure directing agent to decompose, into two or more fragments and removing the fragments from the molecular sieve at a temperature below the temperature that would cause the structure directing agent or its fragments to decompose.
Also provided in accordance with this invention is a method of making a microporous solid comprising:
(a) preparing a reaction mixture comprising at least one active source of reactants required to produce the microporous solid, a structure directing agent capable of forming said microporous solid, an amine component comprising at least one amine containing one to eight carbon atoms, ammonium hydroxide and mixtures thereof, and sufficient water to shape said mixture into a self-supporting shape;
(b) heating said reaction mixture at crystallization conditions and in the absence of an external liquid phase for sufficient time to form the microporous solid containing the structure directing agent and the amine component; and
(c) removing the amine component from the pores of the molecular sieve at a temperature below the temperature that would cause the structure directing agent or the amine component to decompose; and
(d) cleaving the structure directing agent, at a temperature below the temperature that would cause the structure directing agent to decompose, into two or more fragments and removing the fragments from the molecular sieve at a temperature below the temperature that would cause the structure directing agent or its fragments to decompose.